Field of the Invention
The present invention relates generally to the construction of intravascular catheters. More particularly, the invention relates to intravascular catheters having guidewire receptacles which are compatible with distal housings having internal components therein.
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheroma or plaque, on the walls of blood vessels. Such deposits occur both in peripheral blood vessels that feed the limbs of the body and coronary blood vessels which feed the heart. When deposits accumulate in localized regions of a blood vessel, blood flow is restricted and the person's health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty where a balloon-tipped catheter is used to dilatate a region of atheroma, atherectomy where a blade or other cutting element is used to sever and remove the atheroma, and laser angioplasty where laser energy is used to ablate at least a portion of the atheroma. In addition to such therapeutic approaches, a variety of techniques for transluminal imaging of atheroma and other diseased regions of a blood vessel have been proposed, including endoscopic imaging techniques and ultrasonic imaging techniques. Common to all such techniques is the use of an intravascular catheter which is positioned at a desired location within the blood vessel to be treated or imaged.
Two alternative approaches may generally be employed to achieve such positioning. In the first approach, the vascular catheter is provided with a "fixed guidewire" secured to its distal end. The fixed guidewire is typically a coiled spring or other elongate resilient member having a preformed, curved tip. The catheter can then be guided through branches within the vascular network by rotating the entire catheter, causing the tip of the guidewire to enter a desired branch as the catheter is moved forward. In the second technique, entirely separate "movable guidewire" is employed. The movable guidewire is itself a coiled spring or other resilient elongate member and will generally include a curved tip similar to that provided on the fixed guidewires described above. The vascular catheter being positioned includes a guidewire lumen which generally extends down the center of the entire length of the catheter and is sized to receive the movable guidewire. The movable guidewire is first positioned within the vascular system so that its distal end extends beyond the region of interest, and the intravascular catheter is then inserted over the movable guidewire using the guidewire lumen. Such procedures using movable guidewires are commonly referred to as "over-the-wire" insertional techniques.
The use of movable guidewires enjoys a number of advantages over the use of fixed guidewires. In particular, a movable guidewire allows positioning of relatively large diameter catheters which would be difficult to manipulate using a fixed guidewire. The presence of a movable guidewire also facilitates repositioning of the catheter during use and simplifies withdrawal of the catheter and replacement by either the same catheter or a different catheter.
The use of movable guidewires with certain types of intravascular catheters, however, is problematic. Many catheters have internal components within their distal end for imaging or interventional purposes, and such components can interfere with passage of the movable guidewire through the catheter. The use of movable guidewires has been particularly troublesome with imaging catheters of the type employing ultrasonic elements at their distal end, frequently in combination with rotating mirrors. It is undesirable to penetrate the ultrasonic element thus rendering passage of a movable guidewire through the center of the catheter undesirable. Thus, such catheters have normally employed fixed guidewires at their distal ends.
A second consideration in employing movable guidewires relates to their length. In many catheters, the movable guidewire is received in a lumen which extends the entire length of the catheter body. In order to both insert the catheter and remove the catheter while leaving the movable guidewire in place, it is necessary that the movable guidewire have a length equal to at least twice that of the catheter body. In this way, the proximal end of the guidewire may be held in place at all times while the catheter is being inserted or withdrawn. The use of such long guidewires, however, proved highly inconvenient, requiring manipulation of the guidewire in the catheter at great distances from the patient. To overcome these problems, "monorail" systems have been devised for certain types of catheters, including balloon-tipped catheters and laser hot tip catheters.
In such monorail designs, the guidewire lumen extends through only a very short wire lumen formed at the distal end of the catheter. Thus, the length of the guidewire can be reduced to a length which need only be equal to the length of the catheter plus the short length of the wire lumen at the distal end. Such monorail guidewire lumens, however, have not generally been employed in catheters having mechanical and electrical components in their distal end, such as ultrasonic imaging catheters where the passage of a guidewire, even for a short length, is problematic.
For these reasons, it would be desirable to provide intravascular catheters having alternative receptacle constructions for receiving movable guidewires. It would be particular desirable to provide such intravascular catheters with receptacles for receiving movable guidewires in such a way that interference with the internal components is minimized. Preferably, such guidewire receptacles should provide for monorail operation which facilitates separation of the catheter from the guidewire as the catheter is withdrawn.